Proteomics relates to the large scale study of proteins, with a particular focus in many cases on structure and function. Proteins have proven challenging to study, particularly on such a large scale. Such difficulties are due, in part, to, the high variability in the expression of proteins between cells of different types, as well as between cells of the same type experiencing differential biological interactions. Additionally, a large number of proteins can be expressed from a single gene due to alternative splicing or post translational modifications. It has been estimated that greater than 500,000 proteins are expressed in humans from the approximately 25,000 coding genes in the human genome. Given such enormous numbers of proteins that may be present in a biological sample, studying single peptides or proteins either within a single sample or across a number of samples is a difficult task.
One aspect of proteomics that is particularly difficult pertains to the locating and sequencing of a peptide that is present in a subject due to a medical or other condition that may not be present in the general population or present in significantly altered concentration. Such peptides may also occur at very low quantities in the biological sample, thus further increasing the difficulty of peptide identification. The complexity of this search is further exacerbated because the peptide is often unknown, and thus a search is performed for any peptide differences between the biological sample from the subject of interest and biological samples from a control group in an attempt to find those factors that may mediate, diagnose or predict the condition. Once found, however, such peptide differences may lead to diagnostic or prognostic tests for a particular condition or even subsequent medical treatment to minimize or eliminate the condition or the effects of the condition.